On the nature of the crystallographic disorder in submicrometer particles of Ca (OH)2 produced by vapour phase hydration

Beruto, D.; Spinolo, G.; Barco, L.; Tamburini, Umberto Anselmi; Belleri, G.

doi:10.1016/0272-8842(83)90006-8

Cited by 8 publications

(8 citation statements)

References 5 publications

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“…previously (Beruto et al, 1983) and could be an indication, confirmed here, that in part explains the increased reactivity observed following hydration reactivation. Subsequent formation of carbonate on the surface following D2O exposure (Figure 4b, d) displayed a shift in the band at 1476 to 1487 cm -1 and an increase in intensity.…”

Section: Discussionsupporting

confidence: 87%

Surface and bulk carbonate formation in calcium oxide during CO2 capture

2017

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Calcium looping (CaL), the cyclic carbonation and calcination of limestone, is a prominent carbon capture option considering reduced parasitic energy consumption compared to amine scrubbing. The main issue preventing application is sorbent performance decay during cycling. Therefore hydration and extended carbonation reactivation strategies, as well as synthetic approaches to enhance or sustain reactivity, are of interest. Results of an investigation are presented on the impact of reactivation strategies on carbonate formation through detailed study using in-situ infrared spectroscopy. Surface and bulk carbonate formation regimes were readily distinguished allowing the influence of temporal, hydration and thermodynamic conditions within each regime to be studied. Surface chemistry of CaO during two initial cycles was shown to change. Significantly, it was shown that the CaO surface produced from the calcination of Ca(OH)2 possessed more highly reactive sites compared to the surface produced from CaCO3. The presence of water enhanced bulk carbonate formation at 300 °C and influenced the complexation of surface carbonates during looping. The results are of interest in the CaL community, offering molecular scale explanations for macroscale observations, whilst also informing on the role of humidity in direct air capture and sorption enhanced reaction processes.

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Section: Discussionsupporting

confidence: 87%

Surface and bulk carbonate formation in calcium oxide during CO2 capture

2017

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“…Considering that a similar weight increase typically accompanies the onset of carbonation, 9,15 the latter observation can be explained by the carbonation of a small proportion of amorphous CaĲOH) 2 which can be expected to form during steam hydration. 31,32 As the sample is heated further, the CaCO 3 amount increases to a plateau at 520 °C while no CaO reflections are observed to appear in this period.…”

Section: Evolution Of Sorbent Composition and Impermeable Layer Hypot...mentioning

confidence: 99%

In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)₂

2015

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The dehydration and high temperature carbonation reactions of CaĲOH) 2 are an essential part of a number of existing schemes aiming to apply the thermochemical CaO-CaCO 3 cycle ('Ca Looping') in emerging energy industries such as CO 2 capture, gasification and thermal energy storage. However, the underlying chemical mechanisms are poorly understood and the reaction kinetics exhibit a number of strange features such as the increased thermal stability of CaĲOH) 2 , dubbed "superheating", observed in the presence of CO 2 . In this work, in situ X-ray diffraction (XRD) measurements using a synchrotron source are coupled with full pattern fitting analysis to provide high-resolution and high-accuracy data on the evolution of CaĲOH) 2 crystalline structural parameters during the dehydration and carbonation reactions. This method has allowed new observations to be made that provide insight into the studied reaction mechanisms and disprove existing hypotheses as to the origin of superheating. A new hypothesis, involving the formation of an intermediate and permeable CaĲOH) 2 structure was formulated which can explain the growing body of observations in this area. 7306 | CrystEngComm, 2015, 17, 7306-7315 This journal is

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“…Chaix-Pluchery et al 9 propose that the presence of proton donor species adsorbed on the surface of the Ca(OH) 2 crystals can cause an increase in the temperature of dehydration of Ca(OH) 2 Further, it is thought that the defects formed during hydration can be annealed by thermal treatment of the hydroxide. 10 The annealing of crystal defects that occurs during the superheating of Ca(OH) 2 could be the cause of the observed reductions in attrition rates induced by this step. With this hypothesis in mind a series of experiments, described below, were performed to further explore the phenomenon of SD.…”

Section: Introductionmentioning

confidence: 99%

Ca(OH)₂ Superheating as a Low-Attrition Steam Reactivation Method for CaO in Calcium Looping Applications

Materić¹,

Edwards²,

Smedley³

et al. 2010

Ind. Eng. Chem. Res.

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Steam hydration of lime is an effective method for restoring CO2 capture activity but gives rise to high particle attrition rates in a fluid bed reactor. This paper describes the phenomenon of Ca(OH)2 superheating, also referred to as superheated dehydration (SD). The potential of an attrition-free lime reactivation process using this phenomenon is also investigated. Attrition rates of the sorbent are measured when a reactivation step using steam hydration is implemented every three carbonation/calcination cycles. It has been shown that the presence of CO2 during the dehydration step reduces attrition during subsequent cycles. Experiments performed in a small fluid bed reactor show that the presence of 40−100% CO2 during the dehydration step increases the initiation temperature of the decomposition of Ca(OH)2 from 445 to 618 °C. The thermodynamic equilibrium water vapor pressure for the dehydration reaction at 618 °C is 516 kPa, whereas no water vapor was detected in the reactor during the dehydration step before the temperature reached 618 °C. Under these circumstances it is proposed that the Ca(OH)2 is in a nonequilibrium “superheated state”. A CO2 capture cycling experiment, with a reactivation step every three carbonation/calcination cycles, maintained an average activity of 60%, creating only 3.25% of fines < 150 μm after 28 carbonations. The reactivation step consisted of hydrating the sorbent at a temperature of 270 °C and dehydrating it in 100% CO2 with a 23 min hold at 520 °C. It is proposed that the SD phenomenon may be a key step in the development of an industrially feasible method of lime reactivation for use in CO2 capture and in thermal energy storage applications.

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On the nature of the crystallographic disorder in submicrometer particles of Ca (OH)2 produced by vapour phase hydration

Cited by 8 publications

References 5 publications

Surface and bulk carbonate formation in calcium oxide during CO2 capture

Surface and bulk carbonate formation in calcium oxide during CO2 capture

In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)₂

Ca(OH)₂ Superheating as a Low-Attrition Steam Reactivation Method for CaO in Calcium Looping Applications

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On the nature of the crystallographic disorder in submicrometer particles of Ca (OH)2 produced by vapour phase hydration

Cited by 8 publications

References 5 publications

Surface and bulk carbonate formation in calcium oxide during CO2 capture

Surface and bulk carbonate formation in calcium oxide during CO2 capture

In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)2

Ca(OH)2 Superheating as a Low-Attrition Steam Reactivation Method for CaO in Calcium Looping Applications

Contact Info

Product

Resources

About

In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)₂

Ca(OH)₂ Superheating as a Low-Attrition Steam Reactivation Method for CaO in Calcium Looping Applications